In the hot- and cold-rolling of aluminum and other metals, asperities of the workpiece and the rolls are broken off from the matrix due to the ploughing that occurs in the roll bite as the hard steel rolls exert a high shearing force when they traverse the softer metal in the roll bite. These broken off pieces of roll and strip asperities are termed wear debris or "fines". In practice some of the fines remain on the strip as it exits the roll bite while others are washed off into the coolant used to control the roll temperature and roll-bite friction in the rolling process. Because of the large surface area of rolled metal and the large number of asperities found on that area, the amount of fines produced soon turns the coolant black in color and if not removed, could lead to operational problems with the coolant and surface quality problems with the metal being rolled. It is thus necessary to remove the fines to a reasonably low level.
Historically, filtration employing filter aids has been used in the metal rolling industry to accomplish the removal of fines. In the case of rolling mills using water-based fluids, however, because of the chemicals typically used in the oil composition, the fines are coated with a sticky organo-metallic layer that makes filtration through filter aids very difficult. Under the premise that backwashing of filter cartridges employed in filters filtering rolling mill coolant could remove the sticky fines, we attempted to use backwashable filter cartridges to remove the fines. We found that the backwashing of such cartridges was not able to remove the sticky fines from the fibers of the cartridges under normal backwash pressures and the cartridges became plugged. As a result, the filter cycles soon became impracticably short.
Accordingly, there is a need to provide a process by which a filter, which is clogged by the fines obtained by the filtration of lubricating oils, can be regenerated. Once regenerated, the filter will have the performance equivalent to a new filter, at low cost and with no waste liquid disposal problems.